The Gibraltar Arc in the western Mediterranean consists of the Betic and Rif Alpine chains and the Alboran Sea Basin. Four types of stress indicators (wellbore breakouts, earthquake focal plane mechanisms, young geologic fault slip data, and hydraulic fracture orientations) indicate a regional NW–SE compressive stress field resulting from Africa‐Eurasia plate convergence. In some particular regions, deviations of SHmax are observed with respect to the regional stress field. They are gentle‐to‐moderate (22°–36°) anticlockwise rotations located along the North Alboran margin and moderate‐to‐significant (36°–78°) clockwise rotations around the Trans‐Alboran Shear Zone (TASZ). This is a broad fault zone composed of different left‐lateral strike‐slip fault segments running from the eastern Betics to the Alhoceima region in the Rif and resulting in a major bathymetric high in the Alboran Sea (the Alboran Ridge fault zone). Some of these stress rotations appear to be controlled by steep gradients of crustal thickness variation across the North Alboran margin and/or differential loading imposed by thick sedimentary accumulations in basin depocenters parallel to the shoreline. Other stress perturbations may be related to active left‐lateral, strike‐slip deformation within the TASZ that crosscuts the entire orogenic arc on a NE–SW trend and represents a key element to understand present‐day deformation partitioning in the western Mediterranean.

On the basis of the lithospheric structure of the Gibraltar Arc (western Mediterranean), we constrain depth distribution of crustal seismicity and active tectonics by means of rheological modeling. Crustal yield strength and depth of the brittle‐ductile transition zone (BDT) mimic the curvature of the arc with maximum depths of 12–9 km whereas in the Betics and Rif, BDT shallows eastward (to 6–5 km depth), oblique to crustal thickening. Most of the crustal seismicity (>60%) is placed within the brittle crust, decaying exponentially in the ductile crust. Active faults observed in surface geology, control the present topography of the Betics, connect in depth with scattered seismic swarms, and merge into the BDT. This horizon is interpreted as a decoupling horizon that conditions the mode of present‐day deformation partitioning. Below the BDT, low‐strength domains enable crustal flow under central Betics promoting stress rotation and topographic uplift.

[1] We have modeled thermal structure of the crust in the western Mediterranean on the basis of inversion of heat flow and elevation in the context of Airy's isostatic equilibrium. Modeling results reveal dramatic variations in crustal temperatures within the Gibraltar Arc region. The steep gradients in crustal thickness, together with the regional heat flow pattern lie at the origin of temperature anomalies. Temperatures at the base of the crust range between <500°C in the West Alboran Basin, where sediment accumulations exceed 8 km, and >700°C in the eastern Betics and the connection between the Rif and Tell belts in North Africa, where a high heat flow anomaly occurs. High-temperature zones define a hotter region (>650°C) running SW-NE across the central part of the Alboran Sea. These results agree with other geophysical evidence (e.g., low deep-crust V p and P n values) suggesting the occurrence of high temperatures in the deepest crust. According to the estimated silicic composition of the deep crust in the area, temperatures in some regions are appropriate for partial melting under muscovite dehydration conditions (>700°C). We have estimated that average partial melting ranges from $12% (maximum X L ) in the western Tell region to $6% in the eastern Betics. This process modifies physical and mechanical properties of the deep crust enhancing crust-mantle decoupling and deep crustal flow with concomitant surface uplift. These mechanisms explain why high topography and active E-W extension occur transecting the overall orogenic trend of the Gibraltar Arc.